FIG. 3 is a schematic configuration view of a laser machining apparatus for drilling a printed circuit board. FIG. 4 is a plan view of a printed circuit board as a work piece. FIG. 5 is a chart showing an example of a machining program. FIG. 6 is a diagram showing an example of a dot pattern forming characters, which pattern has been registered in an NC unit.
As shown in FIG. 3, a machining apparatus 100 for drilling a printed circuit board is constituted by a machining apparatus body 80 and an NC unit 90. The machining apparatus body 80 has a table 1, a laser oscillator 2, a head portion 3, etc. The table 1 is movable in X- and Y-directions. The NC unit 90 controls the operation of the machining apparatus body 80. A pair of steerable mirrors 4 and an fθ lens 5 are disposed in the head portion 3. A galvanometric control unit 6 controls the positions (rotation angles) of the steerable mirrors 4. A table control unit 7 controls the position of the table 1. A printed circuit board (hereinafter referred to as “workpiece”) 8 is fixed to the table 1.
A laser beam emitted from the laser oscillator 2 is positioned by the pair of steerable mirrors 4, and passed through the fθ lens 5 so as to be incident on the work piece 8 perpendicularly thereto. The time required for moving the table 1 is much longer than the time interval of irradiation with the laser beam or the duration of the irradiation. The machining efficiency can be therefore much higher if the laser beam is positioned by the steerable mirrors 4. The practical size (diameter) of the fθ lens 5 is 50-70 mm. When the diameter of the fθ lens 5 is, for example, 70 mm, the work piece 8 is segmented into regions (hereinafter referred to as “to-be-machined regions”) measuring 50 mm by 50 mm around the central axis of the fθ lens 5 as shown in FIG. 4 (where there are 24 to-be-machined regions segmented by the broken lines) When machining is finished in one to-be-machined region, the table 1 is moved horizontally so that the center of the next to-be-machined region is positioned on the central axis of the fθ lens 5. Such an operation is repeated subsequently till machining is completed all over the to-be-machined regions.
As shown in FIG. 5, central coordinates (portion F in FIG. 5) of each to-be-machined region, central coordinates (portion G in FIG. 5) of each hole to be machined, a instructed character string (portion H in FIG. 5, in which the three characters “ABC” are instructed here), and reference position coordinates (portion J in FIG. 5) for the characters are described in the machining program.
As shown in FIG. 6, each character is designed to be disposed in an area D constituted by squares M with m rows and n columns (for example, 7 rows and 4 columns). The side of each square M measures a. One dot d can be placed in each square M. The center of the square M in the lower left corner of the area D is regarded as a reference position (origin) P0. With reference to the reference position P0, the central coordinates of each dot d forming each character are stored in a storage in advance. When a character string is to be machined, the character string (portion H) and the reference position coordinates (portion J) are instructed. When a character string consisting of a plurality of characters is to be machined, the center of the square M in the lowest left-end corner of the left-end character is regarded as the reference position P0 of the character string. Characters placed adjacent to each other are separated at a distance a. That is, the central coordinates of the dot d referenced by the sign P in FIG. 6 is dP(7a, 3a) by way of example.
Next, a machining procedure to machine characters in the background art will be described.
First, holes in one to-be-machined region are machined based on the instruction of a portion F and a portion G in a machining program. Assume that there is an instructed character string to be machined in the to-be-machined region. In this case, after the holes in the to-be-machined region are machined out, the table 1 is moved based on the description of a portion J, and a reference position P0 of the character string is positioned in the center of the fθ lens 5. The center of each dot d forming each character ABC is irradiated with a laser beam. There may be some characters that cannot be written, that is, the character string may go beyond an end portion of the to-be-machined region. In this case, the characters that can be written in the to-be-machined region are machined out. After that, the table 1 is moved, and the center of the square M in the lowest left-end corner of the first one of the characters that have not been written yet is positioned in the center of the fθ lens 5. Then the characters that have not been written yet are machined. After that, the center of the next to-be-machined region is positioned in the center of the fθ lens 5.
As described above, the time required for moving the table is much longer than the time interval of irradiation with a laser beam or the duration of the irradiation. Accordingly, when the table is moved to machine characters, the time required for moving the table must take part in the machining time. Thus, the machining efficiency cannot be improved.